Heat transfer unit and distillation apparatus embodying same



May 28, 1957 A. LATHAM, JR., EI'AL 2,793,988

HEAT TRANSFER UNIT AND DISTILLATION APPARATUS EMBODYING SAME Filed Sept. 2. 1953 3 Sheets-Sheet i I mm mul K OWWMMLZOU INVENTOR. ALLEN LATHAM,JR. BY8FLO0D EVERETT REEQJI M y 1957 A. LATHAM, JR., ET AL 2,793,988

HEAT TRANSFER UNIT AND DISTILLATION APPARATUS EMBODYING SAME Filed Sept. 2, 1953 s Shee ts-Sheet 2 INVENTOR. L A THA M, JR.

2a ALLEN HFLoo B/ERETT PEE JR.

ATTORNEYS May 28, 1957 A. LATHAM, JR., ET AL 2,793,988

HEAT TRANSFER UNIT AND DISTILLATION APPARATUS EMBODYING SAME Filed Sept. 2, 1953 3 Sheets-Sheet 3 8 6 25? AZ i 1- I 4 2 T a 1- B a j- 7 T 3 =1. Er. INVENTOR.

ALLEN LATHAM R BY 8; FLOOD EVERET TPEEQJE HTTOE/VEYS United States Patent HEAT TRANSFER UNIT AND DISTILLATION APPARATUS EMBODYING SAME Allen Latham, Jr., Jamaica Plain, and Flood Everett Reed, Jr., Littleton, Mass., assignors, by mes-rte assignments, to The Badger Manufacturing Company, Cambridge, Mass., a corporation of Massachusetts Application September 2, 1953, Serial No. 37 8,042

11 Claims. (Cl. 202-187) This invention relates to heat transfer units and method and relates especially to heat transfer units and method used in apparatus for effecting out-of-contact heat exchange between fluids having different temperatures through a wall that maintains the fluids separated from each other. Embodiments and features of the invention further relate to improvements in distillation apparatus of the vapor compression type which result from employment of the above-mentioned units as heat exchange means in distillation apparatus of this type.

One of the principal objects of this invention is the provision of heat transfer units, apparatus and method whereby deposits which tend to form on heat exchange surfaces and which impair heat transfer efficiency may be readily removed in a way which enables this to be accomplished using economically produced equipment and without substantial operating expense or loss of operating time.

Other objects of this invention relate to the attainment of these objectives in the case of heat exchange apparatus of the type comprising a plurality of units or cells arranged in a battery and which is suitable for use as the condenser heat exchanger in the evaporator chamber of distillation equipment of the vapor compression type.

One of the principal features of this invention resides in the provision of a heat transfer unit of the character aforesaid which comprises a flexible plate comprised of resilient material which is maintained bowed so that the centrally disposed portion thereof is substantially spaced from the normal plane of the plate and which is responsive to pressure differential on the opposite sides of the plate so as to move with a snap action from bowed position on one side of said plane to bowed position on the other side of said plane. For maintaining the plate bowed as aforesaid, planar constricting frame means is employed which is substantially continuously curved so that the constricting action imposed by the frame means causes the portion of the plate that is centrally disposed relative to the frame means to be normally maintained in the aforesaid bowed condition. Preferably there are substantially spaced plates secured to a common constricting frame which provide a chamber between said plates and within the frame, each of the plates being maintained bowed by the constricting action of the frame.

For many types of heat transfer applications one of the things that occasions operating difliculty is loss of ethciency of the heat exchange surface due to gradual buildup of scale or other incrustation by deposit thereon from a fluid in contact therewith. Such build-up of scale is especially troublesome in the case of distillation apparatus of the vapor compression type wherein a condenser heat exchanger is used for providing a heated surface in contact with a solution to be distilled and which, during the distillation thereof, tends to form a deposit on the surface of the condenser heat exchanger which gradually builds up and not only impairs the efiiciency of the apparatus but also acts to adversely affect the maintenance of the 2,793,988 Patented May 28, 1957 proper heat balance required for maintaining desired operating conditions.

When heat transfer units of the character aforesaid are provided having wall plates for heat transference therethrough, scale deposits formed on the surfaces thereof may be exfoliated and removed, according to this invention, so that the scale no longer impairs the efficiency of the heat transference, merely by flexing the plate walls of the heat transfer units with attendant snap action in moving from position bowed to one side of the normal plane of the plate to position bowed to the other side of this plane. This can be accomplished merely by varying the relative pressures on the opposite sides of the plate. Thus, in the case of vapor-compression distillation, vapor evolved from solution in a vaporization chamber is compressed to a pressure at which its condensing pressure is above the boiling point of the solution in the vaporization chamber and is condensed in a condenser heat exchanger maintained in contact with boiling solution, the pressure within the condenser heat exchanger being, of course, substantially greater than that within the evaporator chamber. Such conditions may prevail for many hours of operation with attendant gradual build-up of scale from the solution in contact with the surface of the condenser heat exchanger, and as soon as the scale build-up begins to exercise any substantial effect in impairing operating efficiency this condition can be corrected merely by lowering the pressure within the condenser heat exchanger as by the expedient of stopping or slowing down the compressor and by opening up a vent from the condenser heat exchanger. The pressure within the condenser heat exchanger is caused to fall off until the plates of the heat transfer units flex from outwardly bulged position to inwardly bulged position. In some instances the pressure normally maintained within the evaporator chamber may be superatmospheric pressure so that when the pressure within the condenser heat exchanger is reduced to atmospheric pressure or thereabouts the pressure within the evaporator chamber will be substantially greater than the pressure within the condenser heat exchanger, thus promoting the fiexure from the outwardly bowed to the inwardly bowed position. When the snap action occurs more is involved than mere stretching of the surface on which scale has become deposited. By providing heat transfer units comprising one or more metal plates adapted to be moved by a snap action from position bowed to one side of a plane to position bowed on the other side of the plane fiexure that is both large and sudden is afforded without excessive build-up of stress. So long as the wall plate is flexed with a snap action the exfoliation of the scale deposit can be effected very completely and quickly, and when this has been accomplished the pressure within the condenser heat exchanger is merely restored to that which is normally maintained with resultant fiexure of the unit walls with a snap action to the normally outwardly bowed position. In this way the efliciency of the apparatus can be quickly and easily restored to that which prevailed prior to substantial formation of the scale deposit.

It is apparent that exfoliation of scale from heat transfer units embodying this invention may be effected with no greater trouble or expense than that required for shutting off the compressor and opening a valve. Moreover, the exfoliation of the scale and the restoration of the efficiency of the apparatus may be effected with only a negligible interruption of operational output of the apparatus.

Further features and advantages of this invention relate to the provision of such units in the form of a horizontally disposed battery with headering means for entering and effluent fluids. Thus in the case of condenser heat exchange means according to this invention adapted for condensation of vapor therein with resultant release of heat of vaporization, means are preferably provided for directing vapor from a vapor source successively through a series of chambers comprised in a battery and for preventing escape of non-condensable gases from the chambers of the series except from a chamber at the end of the series that is remote from the chamber into which the vapor is initially introduced for sequential travel through the series. Other features relate to the provision of headering means whereby the individual headers and units secured thereto are adapted for arcuate group disposition and whereby passage means is provided within the assembled headers for directing vapor successively through a plurality of the units.

Further objects, features and advantages of this invention will be apparent from the following description of apparatus that illustrates the practice of this invention in connection with a typical embodiment comprised in distillation apparatus of the vapor-compression type as shown in the accompanying drawings, wherein:

Fig. l is an essentially schematic vertical section of one type of vapor-compression distillation apparatus wherein heat transfer unit means according to this invention is employed;

Fig. 2 is a perspective view of a battery of a plurality of the heat transfer units according to this invention as used in the distillation apparatus shown in Fig. 1;

Fig. 3 is a schematic showing of the action of the headering arrangement in directing vapor into and with drawing condensate from the heat transfer units;

Fig. 4 is a side elevational view on a larger scale of a single heat transfer unit according to this invention which is of the type shown in Figs. 1 and 2;

Fig. 5 is an edge elevation of the left-hand edge of the unit shown in Fig. 4;

Fig. 6 is a top view of the unit shown in Figs. 4 and 5;

Figs. 7 and 8 are, respectively, sections taken on the lines 77 and 88 of Fig. 4;

Fig. 9 is a section taken in the plane A-A of Fig. 4 showing the side Walls of the unit in outwardly bowed position; and

Fig. 10 is similar to Fig. 9 except that side walls of the unit are shown in inwardly bowed position.

In the accompanying drawings the apparatus shown illustrates the features of this invention which relate both to the heat transfer unit as such and to the use of such units in vapor-compression distillation apparatus.

Referring to Fig. l, the distillation apparatus of the vapor-compression type is shown as comprising the evaporator chamber into which solution to be distilled is fed by the lines 16 and 17, the solution being preheated in the preheater heat exchanger 18. Vapor evolved from the solution in this evaporator chamber 15, after passing through the liquid-vapor separator 19, is taken into the compressor 21 by the line 20. Vapor which has been compressed by the compressor 21 until its condensing temperature is substantially above the boiling point of the solution in the evaporator chamber is directed therefrom by the high pressure vapor line 22 and branch lines 23 and 23a to the condenser heat exchanger means which is indicated generally by the reference character 24 and which will be described more in detail hereinbelow in connection with Figs. 2 to 10.

In the condenser heat exchanger 24 the compressed vapor condenses in out-of-contact heat exchange relation with the solution in the vaporization chamber, thus giving up its latent heat of vaporization as well as some of its sensible heat for heating and boiling the solution. If desired, auxiliary heating means (not shown) may be used to make up for heat losses, and, if desired, heat losses may he held down by surrounding the vaporization chamber with a layer of heat insulation material (not shown). The distillate that is formed in the condenser heat exchanger means 24 is directed by the distillate header 25 to which the individual cells or units are connected by the draw-01f lines 26, except that in the preferred battery construction certain of the individual cells or units are connected to the vent header 27 for reasons which will be explained hereinbelow particularly in connection with the description of Fig. 3. The distillate is directed from the header 25 by the line 28 to the distillate-collecting container 29 from which any non-condensable gases such as air that have been carried thereto can be vented by means of the line 30, which is controlled by the valve 31. Distillate is removed from the system by the lines 32 and 33, it being passed through the preheater heat exchanger 18 so as to preheat incoming feed. The liquid level in the distillate-collecting container is controlled by the float valve 34 in the line 32.

The line 35 serves to determine liquid level of the solution in the evaporator chamber 15 and to direct it to the concentrated solution-collecting container 36. Any liquid separated from the vapor by the liquid-vapor separator 19 is also directed to this container by the line 37. The concentrated solution is directed from the container 36 by the lines 38 and 39, the liquid level in the container 36 being controlled by the float valve 40 in the line 38 and the efiluent concentrated solution preferably being used to assist in preheating the incoming feed in the preheater heat exchanger 18.

In the embodiment shown the individual heat transfer units or cells, which are indicated generally by the reference character 41, are shown in Fig. 2 as comprised in a battery of forty of the cells, and the structure thereof is shown more in detail in Figs. 4 to 10.

For purposes of illustration, the units more particularly described below are suitable for being comprised in the condenser heat exchanger of a vapor-compression distillation unit adapted for use in the distillation of potable water from sea water. Each cell is in the form of an ellipse whose inner dimensions are about 9 inches and 5 inches for the major and minor axes respectively, and whose thickness is about inch. Each cell is provided by a stout elliptical frame member 42 which may be approximately V2 inch in thickness from the inner surface to the outer surface. To the side surfaces of this frame member there are secured, as by welding, flexible plates 43 which may desirably be Monel sheet metal substantially 0.021 inch in thickness. During the fabrication of the cells or units the plates 43 are held deformed so that when they are welded to the frame member 42 frame member 42 continues to exert a constricting action on the plates 43 whereby each of the plates, instead of being flat, is held bowed so that the portion thereof that is disposed centrally with respect to the frame member is substantially spaced from the plane of the plate where it is welded to the frame member. The bowing of the plates 23 is shown in Figs. 9 and 10, the plates being bowed outwardly in Fig. 9 and inwardly in Fig. 10. Since the plates 43 are composed of resilient material, they can be moved from outwardly to inwardly bowed positions and vice versa responsive to change in the relative pressure on the opposite sides of the plates. Moreover, as the plates pass from one bowed position to the other they do so with a snap action. While it is not essential to do so, the plates 43 may be provided with the extensions 43a for the purpose of providing auxiliary mechanical support for the condensate lines 26 so as to reduce the stress at the joints between the lines 26 and the frame members 42.

While each of the cells or units is complete in itself as a heat transfer means, a plurality of them are ordinarily employed as disposed in a battery and in the apparatus shown the condenser heat exchanger 24 has been shown as comprised in a battery of forty of the units which are arranged with the shorter axes thereof substantially in a horizontal plane and with the cells disposed so as to provide an annular arrangement.

The header means for introducing vapor into the cells is made so that the vapor is passed through four groups of ten cells each, the vapor being passed in series through the cells of each group. The arrangement of two such groups is indicated schematically in Fig. 3, and while only four cells have been shown in each group, the other cells of each group are to be assumed as present, as indicated by the break. Thus when vapor is passed from the compressor 21 by the line 23a it is directed initially into the first cell 41x of each group and then in series through the successive cells to the last cell 41y of each group. For providing headering means for accomplishing the function or action shown in Fig. 3 when the cells are arranged as shown in Fig. 2, each of the cells is provided with a horizontally tapered header element 44 whose side faces are adapted to fit in abutting relation as shown in Fig. 2. The interior of these header elements has passages therein, as typically shown in Figs. 4, 6, 7 and 8, so as to provide a first passage 45 that communicates between the interior of the cell and one side face of the header element and a second passage 46 that communicates between the interior of the cell and the opposite face of the header element. Each header element that adjoins each side face of the header element shown is similarly provided with passage means that register with the passages shown so that there may be continuous passage means between one cell and the next for successive travel of vapor through the series of ten cells in each group as schematically shown in Fig. 3. The header element of the first cell in each group is adapted to be connected to the conduit 23 or 23a, as the case may be, and the header element for the last cell of each series merely is provided with passage means for directing vapor into the cell from the adjoining cell of the series and does not have any passage means for directing vapor from this cell, except possibly through the distillate withdrawal line therefor.

The header elements as a group are held in the annular grouping with the interfaces between the side faces thereof in pressure contact by the band 53 which may be tightened into place by the clamping means 51. For assisting in the alignment of the header elements, the side faces thereof may have holes 52 drilled therein for dowel pins interposed between successive header elements A liquid and vapor-tight seal between successive header elements may be provided by light gasketing.

It is the distillate that is formed in the first nine cells of each series of ten cells that is drained therefrom into the distillate header 25 by the lines 26, while the distillate from the tenth cell of each series is taken off into the vent header 27. The distillate contained in distillate header 25 is prevented from flowing directly therefrom to the distillate-collecting container 29 by the rise 47 in the line 28 which during operation has the effect of maintaining a water seal leg 48 in the draw-off line 26 of each of the first nine cells of each series. As a result, all uncondensed vapor that is directed into these cells 41 by the successive header elements 44 is caused to be passed along successively through the cells of each series, rather than have a portion thereof by-passed into the condensate collection system; and in this way sufficiently high velocity of vapor through the different cells may be maintained for carrying along any non-condensable gases such as air from cell to cell to the tenth cell from which the noncondensable gases may be taken along with the distillate through the line 49 into the vent header 27 from which distillate drains into the distillate-collecting container 29 by virtue of the connection 50 of the vent header with the line 28 beyond the water seal. The non-condensable gases are vented from the chamber 29 by the line 30 controlled by the valve 31, as mentioned hereinabove, the valve 31 being adjusted so as to ensure the desired pres sure being maintained within the condenser heat exchange units 41.

By way of illustration, the heat transfer units or cells as described above were used in evaporating sea water while maintaining the boiling sea water at a gauge pressure about 15 pounds per square inch and the steam within the units at a gauge pressure of about 27 pounds per square inch. Under these maintained conditions scale tended to build up to a thickness of abou his inch over a period of seven days continuous operation and the overall heat transfer rate thereafter began to fall off rapidly. However, instead of permitting this further build-up of scale the operation was carried out so that at the end of each period of seven days the pressure within the cells was permitted to drop. During normal operation the walls of the cells were bowed outwardly to the convex position illustrated in Fig. 9. However, when the pressure within the units was permitted to drop the change in the relative pressure resulted in the walls of the cells moving with a snap action from the convex position illustrated in Fig. 9 to the concave position indicated in Fig. 10; and when the pressure within the units was restored to the normally maintained operating pressure condition, the walls of the cells returned with a snap action to the position indicated in Fig. 9. One such flexing of the walls of the cells was sufficient to exfoliate substantially all of the scale that had been deposited on the active part of the wall surface and the heat transference characteristics were in each case restored so that for each period the behavior characteristics were essentially the same as during the initial period.

It is apparent from the foregoing that by stopping or slowing down the compressor and opening the valve 31 in the vent line 30, the flexing of the side walls of the cells to exfoliate scale therefrom can be effected quickly; and immediately thereafter production can be resumed. It is normally desirable in the practice of this invention that the space in the evaporator chamber below the condenser heat exchanger be such as to provide a copious sump for receiving exfoliated scale so that the apparatus may be operated for a very long period without the necessity for a shut-down for cleaning out exfoliated scale.

In accomplishing the exfoliation of the scale, the snap action effects such suddenness of velocity change that the deposited scale is effectively dislodged. Moreover, the action of the frame member in constricting the side walls of the cells so that they are normally buckled or bowed has the effect of distributing the resulting strain with a high degree of uniformity so that retention of scale in localized unstrained areas is minimized. In order that the stress concentrations may be suited for the desired snap action and exfoliation of scale, the constricting frame means therefor should be substantially continuously curved, as distinguished from being angular, or comprising irregularly disposed discontinuous or reverse curves. Preferably, the constricting frame means is continuously rounded so as to be elliptical, as shown, or round. The frame means should be sufficiently strong in relation to the side wall plates so as to be adapted to maintain the side walls buckled against the resilient force of the deformed material of which they are comprised which, except for the constricting force exerted by the frame, would tend to restore the side walls to their unstressed shape.

It is believed to be apparent from the foregoing that problems resulting from scale formation have been suc cessfully solved by means which not only is inexpensive as regards installation but also requires extremely little in the way of operational expense while maintaining a high order of heat transfer efliciency.

While this invention has been described in connection with a specific embodiment thereof, it is to be understood that this has been done for illustrative purposes and that embodiments thereof may take many different forms. Moreover, while certain features of this invention relate to its employment in distillation apparatus of the vapor compression type, it likewise is adapted to be employed whenever out-of-contact heat transference is desired between two fluids.

We claim:

1. A heat transfer unit for use in maintaining a fluid in out-of-contact heat exchange relation with another fluid which comprises a chamber having inlet means for directing a fluid into said chamber and outlet means for directing fluid out of said chamber, a flexible plate that constitutes a wall of said chamber and is adapted to maintain a fluid within said chamber in out-of-contact heat exchange relation with a fluid in contact with the other side of said plate on the exterior of said chamber, and planar substantially continuously curved constricting frame means for said plate by marginal construction imposed thereon by said frame means which maintains said plate normally bowed so that the centrally disposed portion of said plate within said frame means is substantially spaced from the plane of said plate at said frame, said plate being comprised of resilient material that is movable while said plate is marginally constricted by said frame means between bowed position as aforesaid on one side of said plane to bowed position as aforesaid on the opposite side of said plane with a snap action upon passing through said plane responsive to change of relative pressures on the opposite sides of said plate.

2. A heat transfer unit for use in maintaining a fluid in out-of-contact heat exchange relation with another fluid which comprises a chamber having substantially spaced flexible plates secured to a common substantially continuously curved planar constricting frame therefor which maintains each of said plates normally substantially bowed so that the centrally disposed portion thereof within said frame is substantially spaced from the plane of said plate at said frame and each of said plates being comprised of resilient material that is movable while maintained as aforesaid by said constricting frame between bowed position as aforesaid on one side of said plane to bowed position as aforesaid on the other side of said plane with a snap action upon passing through said plane responsive to change of relative pressures on the opposite sides thereof, means for directing a fluid into the space between said plates within said frame, and means for directing a fluid from said space.

3. A heat transfer unit according to claim 2 wherein said frame is substantially elliptical.

4. A heat transfer unit according to claim 2 wherein said frame is substantially round.

5. A heat transfer device comprising a plurality of chambers each having normally substantially vertically disposed substantially spaced flexible side wall plates secured to substantially continuously rounded constricting frame means therefor which maintains each of said plates bowed so that the centrally disposed portion thereof with in said frame means is substantially spaced from the plane of said plate at said frame, each of said plates being com prised of resilient material and adapted to have said centrally disposed portion thereof moved from one side to the other of said plane with a snap action responsive to relative change of pressure on the opposite sides thereof, and said chambers being comprised in a normally substantially horizontally disposed battery, a fluid-holding container within which said chambers are so disposed. means for supporting said chambers so disposed within said container with the external surfaces thereof in con tact with fluid held in said container, means for directing fluid into said chambers of said battery, means for directing fluid from said chambers means for normally maintaining fluid within said chambers under substantially higher pressure than that of the fluid in said container in contact with the external surfaces of said chambers, and means for effecting reduction of pressure of fluid within said chambers in relation to the pressure of fluid in contact with the external surfaces of said chambers to a pressure substantially below the pressure of fluid in contact with the external surfaces of said chambers.

6. A heat transfer device according to claim 5 wherein said means for directing a fluid into said chambers comprises means for directing vapor from a vapor source successively through a series of said chambers, and wherein said means for directing fluid from said chambers comprises draw-off line means for withdrawing from adjacent the bottom of each of the chambers of said series condensate resulting from condensation of said vapor therein, means for maintaining a liquid seal in said drawoff line means that is effective to prevent escape of noncondensable gases or vapor from said chambers of said series through said draw-off line means except for the chamber at the end of said series remote from the chamber of said series into which said vapor is initially introduced for sequential travel through said series of chambers.

7. A heat transfer device according to claim 5 wherein a plurality of adjoining chambers of said battery each has a header element secured thereto adjacent the upper portion thereof, a plurality of said header elements presenting abutting side surfaces that are disposed substantially in planes that radiate from a common substantially vertical axis for arcuate group disposition of said elements and of the chambers secured thereto and said header elements comprising adjacent header elements having passage means therein which when said side surfaces are in abutting relation are in registration for providing continuous passage means communicating between adjacent chambers for permitting passage of vapor from one to the other of said adjacent chambers.

8. A heat transfer device according to claim 5 which comprises means for introducing vapor from a vapor source into one of said chambers and means for directing vapor from said chamber for travel in succession into and from each of a plurality of additional chambers.

9. In a vapor-compression distillation apparatus comprinting an evaporator chamber, a compressor, means for directing vapor from said evaporator chamber to said compressor, a condenser heat exchanger within said evaporator chamber adapted to maintain a fluid in out-ofcontact heat exchange relation with solution in said evaporator chamber, means for directing compressed vapor from said compressor into said condenser heat exchanger, means for maintaining the pressure of vapor introduced into said condenser heat exchanger from said compressor at a pressure during condensation thereof substantially greater than that prevailing in said evaporator chamber, means for directing condensate from said condenser heat exchanger, means for introducing solution to be distilled into said evaporator chamber, and means for withdrawing concentrated solution from said evaporator chamber; the improvement which comprises a flexible plate comprised in said condenser heat exchanger disposed for maintain ing fluid within said condenser heat exchanger in out of Contact heat exchange relation with solution within said evaporator chamber, a substantially continuously curved constricting frame secured to said plate which maintains said plate outwardly bowed so that the centrally disposed portion of said plate within said frame is substantially spaced from the plane of said plate at said frame in the direction toward solution in the evaporator upon operation of said compressor to maintain a pressure within said condenser heat exchanger greater than that within said evaporator chamber, said plate being comprised of resilient material and being adapted to have said centrally disposed portion thereof moved between outwardly and inwardly bowed positions with a snap action responsive to successive lowering and raising of the pressure of vapor within said condenser heat exchanger.

if). In a vapor-compression distillation apparatus comprising an evaporator chamber, a compressor, means for directing vapor from said evaporator chamber to said compressor, a condenser heat exchanger mounted within said evaporator chamber adapted to maintain a fluid in out-of-contact heat exchange relation with solution in said evaporator chamber, means for directing compressed vapor from said compressor into said condenser heat exchanger, means for maintaining the pressure of vapor introduced into said condenser heat exchanger from said compressor at a pressure during condensation thereof substantially greater than that prevailing in said evaporator chamber, valve controlled vent-line means for effecting lowering of the pressure maintained within said condenser heat exchanger by acuation of said valve, means for directing condensate from said condenser heat exchanger, means for introducing solution to be distilled into said evaporator chamber, and means for withdrawing concentrated solution from said evaporator chamber; the improvement which comprises a battery of vertically disposed cells comprised in said condenser heat exchanger in operatively connected relation with said means for directing compressed vapor from said compressor into said condenser heat exchanger and with said means for directing condensate from said condenser heat exchanger, each of which cells comprises substantially spaced flexible plates secured to a common substantially continuously rounded constricting frame therefor which maintains each of said plates normally bowed outwardly so that the centrally disposed portion thereof within said frame is substantially spaced from the plane thereof at said frame in the direction toward solution in the evaporator chamber upon operation of said compressor for maintaining a pressure within said cells substantially greater than that within said evaporator chamber, each of said plates being comprised of resilient material and being adapted to have said centrally disposed portion moved between said 10 outwardly and inwardly bowed positions with a snap action responsive to lowering and raising of pressure of vapor within said condenser heat exchanger.

11. Vapor-compression distillation apparatus according to claim 10 wherein said cells are elliptical with the longer axis disposed vertically and with the shorter axis disposed substantially in a common horizontal plane, wherein said means for directing vapor from said compressor to said condenser heat exchanger comprises header means adjacent the top of said cells for directing ingress of vapor compressed by said compressor into said cells, and said means for directing condensate from said condenser heat exchanger comprising header means adjacent the bottom of said cells into which condensate flows from said cells.

References Cited in the file of this patent UNITED STATES PATENTS 455,925 Neuhauss et al July 14, 1891 838,195 Le Sueur Dec. 11, 1906 1,180,947 Scott Apr. 25, 1916 1,521,147 Benjamin Dec. 30, 1924 1,604,397 Ercanbrack Oct. 26, 1926 1,966,938 Stone July 17, 1934 2,449,587 Chambers Sept. 21, 1948 2,487,884 Lunt Nov. 15, 1949 FOREIGN PATENTS 606,028 Germany Nov. 23, 1934 

9. IN A VAPOR-COMPRESSION DISTILLATION APPARATUS COMPRINTING AN EVAPORATOR CHAMBER, A COMPRESSOR, MEANS FOR DIRECTING VAPOR FROM SAID EVAPORATOR CHAMBER TO SAID COMPRESSOR, A CONDENSER HEAT EXCHANGER WITHIN SAID EVAPORATOR CHAMBER ADAPTED TO MAINTAIN A FLUID IN OUT-OF CONTACT HEAT EXCHANGE RELATION WITH SOLUTION IN SAID EVAPORATOR CHAMBER, MEANS FOR DIRECTING COMPRESSED VAPOR FROM SAID COMPRESSOR INTO SAID CONDENSER HEAT EXCHANGER, MEANS FOR MAINTAINING THE PRESSURE OF VAPOR INTRODUCED INTO SAID CONDENSER HEAT EXCHANGER FROM SAID OCMPRESSOR AT A PRESSURE DURING CONDENSATION THEREOF SUBSTANTIALLY GREATER THAN THAT PREVALING IN SAID EVAPORATOR CHAMBER, MEANS FOR DIRECTING CONDENSATE FROM SAID CONDENSER HEAT EXCHANGER, MEANS FOR INTRODUCING SOLUTION TO BE DISTILLED INTO SAID EVAPORATOR CHAMBER, AND MEANS FOR WITHDRAWING CONCENTRATED SOLUTION FROM SAID EVAPORATOR CHAMBER; THE IMPROVEMENT WHICH COMPRISES A FLEXIBLE PLATE COMPRISED IN SAID CONDENSER HEAT EXCHANGER DISPOSED FOR MAINTAINING FLUID WITHIN SAID CONDENSER HEAT EXCHANGER IN OUT-OFCONTACT HEAT EXCHANGER RELATION WITH SOLUTION WITHIN SAID EVAPORATOR CHAMBER, A SUBSTANTIALLY CONTINUOUSLY CURVED CONSTRICTING FRAME SECURED TO SAID PLATE WHICH MAINTAINS 